1. Field of the Invention
This invention relates to the field of lamina replacement.
2. Description of the Related Art
Laminectomies, removal of the spinal lamina, are the most common surgical procedures in spinal surgery. Laminectomies are routinely performed in the cervical and lumbar spine to allow decompression of key areas of the spine.
Cervical laminectomies allow decompression of the spinal cord and nerve roots. Patients may present with a radiculopathy (pain in the arms), myelopathy (weakness in arms and legs), or a combination of both. Cervical laminectomies are performed over multiple cervical levels and are an effective technique for cervical decompression and relief of symptoms. Removal of the posterior spinal elements, the cervical lamina, predisposes the patient to develop spinal instability, deformity, and pain. The posterior spinal elements, lamina, allow posterior structural support for the spine and an attachment for the posterior neck muscles. Some surgeons will perform a spinal fusion after cervical laminectomy to prevent spinal deformity. Cervical fusion creates an unnatural state for the neck, however, as the entire fused neck segment is non-mobile. There is a high risk of adjacent level segment instability after cervical fusion since all of the force with motion is transferred to the segment above and below the fusion.
Cervical laminoplasty has been devised for decompression and reconstruction of the cervical lamina, but has certain limitations that have decreased its usefulness in spinal surgery. The primary issue is the technical difficulty of cervical laminoplasty. A “trough” needs to be drilled on one side of the junction of the lamina and lateral mass. This is a technically challenging technique. After a complete trough is formed on one side of the lamina-lateral mass junction, a partial trough is then formed on the opposite side. The lamina is then lifted off the dura and a wedge of bone is secured between the lifted-up side of the lamina Therefore, current cervical laminoplasty techniques allow adequate decompression of only one side of the spinal cord and nerve roots.
Lumbar laminectomies are performed for decompression of the cauda equina and nerve roots. As a large laminectomy defect is created, however, spinal instability can occur. There can also be additional scar formation, as the muscle has to rest directly on the dura after a traditional laminectomy. Some surgeons use hemilaminotomies, where only a portion of the lamina is removed to decompress the nerve roots. However, hemilaminotomies are technically difficult, time consuming, and cannot adequately decompress the bilateral nerve roots and central dura. Lumbar fusions are routinely performed after lumbar laminectomies, but represent a plethora of technical difficulties and predispose the patient to “adjacent level” instability as forces are displaced above or below the fusion. A fusion also involves the placement of large pedicle screws through the pedicle of the vertebral body. Misplacement of the screws has resulted in cerebrospinal fluid (CSF) leaks, nerve injury, and paralysis.
As such, there is still a need for a prosthetic implant for restoring the lamina after laminectomies while providing complete relief for the patient.